Code organization

ruby-talk
1

Hi all,

What are the differences bewteen the following code organization?
What situations are preferred by each one?

Thanks,

Li

#######code 1#############
module A
   class B end
   class C end
end

#######code 2#############
class B
   include module A
end

class C
  include module A
end

···

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2

Li Chen wrote:

What are the differences bewteen the following code organization?
What situations are preferred by each one?

In code 1, module A is just acting as a namespace, so that you have two
classes, A::B and A::C. This is useful to ensure that your class names
don't stomp on anyone else's use of the same names. All you have to do
is ensure name A is unique.

Code 2 doesn't run as it stands, so you need to rewrite as:

module A; end

class B
   include module A
end

class C
  include module A
end

In this case, instance methods defined in module A are available in both
class B and class C. This is almost the same as subclassing B and C from
class A. B and C also get access to any constants defined in the A
namespace, without needing the A:: prefix.

So in summary: they achieve two completely different ends (namespace
separation, and method sharing, respectively)

···

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3

Hi all,

What are the differences bewteen the following code organization?
What situations are preferred by each one?

Thanks,

Li

#######code 1#############
module A
   class B end
   class C end
end

#######code 2#############
class B
   include module A
end

class C
  include module A
end

They are totally different, and they illustrate the two main purposes of
a module. Neither is legal as you have it so I will change the code to
make it legal.

##### 1 ######

module A
   class B
   end
end

A is a namespace, so you must say A::B from outside module A to refer to
B.

##### 2 #####

module A
   def hello
     p "howdy"
   end
end
class B
  include A
end
B.new.hello

Module A's instance methods are copied into class B as instance methods
("mixin").

m.

···

Li Chen <chen_li3@yahoo.com> wrote:
A::B.new

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4

Brian Candler wrote:

So in summary: they achieve two completely different ends (namespace
separation, and method sharing, respectively)

Hi Brian,

Thank you so much.

As I recall correctly module has two major funtions/purposes:
1) namespace separation 2) mixin. So you mean in the second code it
works as a mixin or method sharing?

Li

···

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5

Li Chen wrote:

As I recall correctly module has two major funtions/purposes:
1) namespace separation 2) mixin. So you mean in the second code it
works as a mixin or method sharing?

Yes, mixin or method sharing (two terms to describe the same thing)

Re-reading, there's another error I didn't fix in that example: it
should say "include A" not "include module A"

···

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